Preheat oven to 350 degrees F (175 degrees C). Grease a 9 inch round cake pan.
Combine the rice flour, tapioca flour, sugar, baking soda, baking powder, and salt in a large bowl. In a separate bowl, whisk together egg and buttermilk . Make a well in the center of the dry ingredients and pour in the wet. Stir just until the dry ingredients are moistened. Pour into the cake pan.
Bake for 65 minutes in the preheated oven, or until a toothpick inserted into the center comes out clean. Cool on a wire rack, for 10 minutes before removing from the pan. Wrap bread in plastic wrap or aluminum foil and let stand overnight for the best flavor.
